Ultrasound imaging has provided useful information about the interior characteristics of an object or subject under examination. In general, an ultrasound scanner includes a transducer array with transducer elements that receive echoes (acoustic signals) reflected from structure in a field of view. In B-mode imaging, the echoes are beamformed to generate scanlines, which are processed to generate a scanplane, or a two dimensional image of the field of view, which can be visually displayed through a display monitor.
The beamforming operation has included a “delay-and-sum” operation. An example is discussed in connection with FIG. 1. In FIG. 1, circular acoustic waves 102, 104, 106, etc. reflected from a focus region 108 propagate towards and arrive at different times at a transducer array surface 110 of transducer elements 1121, . . . , 112N. For the circular acoustic wave 102, a central region 114 arrives first at a centrally located element (e.g., the element 112) and peripheral regions 116 arrive last at end elements (e.g., the elements 1121 and 112N).
The transducer elements 112 produce analog RF signals which are respectively amplified by amplifiers 1181, . . . , 118N. The amplified signals are respectively delayed by elements 1201, . . . , 120N so that the amplified signals reach the output of the delay elements 1201, . . . , 120N at approximately a same time. The delayed signals are then summed with an adder 122. By delaying all of the signals, reception is focused at the focus region 108. The delay processing has been performed in the digital domain and in the analog domain.
FIG. 2 shows an example of implementing delays in the digital domain. In FIG. 2, the amplified analog RF signals are converted, via analog-to-digital converters (ADCs) 2021, . . . , 202N to digital signals. The digital signals from the ADCs 2021, . . . , 202N are digitally processed to introduce the delays, and the digitally delayed signals are summed, producing a digital beam sum. With this approach, each element 1201, . . . , 120N requires its own ADC 2021, . . . , 202N.
Unfortunately, the ADCs 2021, . . . , 202N are relatively large and high power consuming components. Furthermore, the digital beam summing network generally requires a coarse-delay shift register and a fine-delay interpolating circuit. Such circuitry may consume a substantial amount of power and space in the ASIC/FPGA for each data channel. As such, this implementation may have limited opportunities, especially when implemented in a low power ultrasound imaging device.
FIG. 3 shows an example of implementing delays in the analog domain. In FIG. 3, the amplified analog RF signals are summed in an inductive-resistive-capacitive (LRC) delay line 302 with staggered inputs, where the signal from a center amplifier 1181 delayed the longest, and the signals from the outer channels 1121 and 112N are delayed the shortest. The LRC delay line 302 outputs an analog beam sum. Unfortunately, this approach uses LRC delay lines, which are costly and not well suited for high density ASICs, with the inductive element placed outside of the ASIC.